Polysilicon of the type disclosed in the above-identified applications is composed of free flowing, approximately spherical particles. These particles can be transported and handled readily. Hence, such bead-like products offer crystal growers a product that is tailor-made for development of continuous melt replenishment systems used in production of monocrystalline silicon. Monocrystalline silicon is used in the production of semiconductor devices.
For a description of the polysilicon and process provided by Messrs. Gautreaux and Allen, the above-cited applications are incorporated by reference herein, as if fully set forth.
This invention relates to an upgrading improvement in the polysilicon disclosed in the above-mentioned applications. In a continuing effort to improve such polysilicon, it has been discovered that such product can be improved by a heat treatment which reduces the content of a volatile impurity, which is believed to be hydrogen.
Applicants are unaware of any prior art relating to hydrogen removal from polysilicon. Sanjurjo et al, U.S. Pat. No. 4,676,968 discloses a process for melt consolidating polysilicon powder. For melt consolidation, the powder is heated at a temperature above the melting point of silicon. (1410.degree. C.). The processes of this invention do not employ temperatures above silicon's melting point. Furthermore, an object of this invention is to produce heat treated polysilicon while avoiding melt consolidation. Accordingly, the processes of this invention markedly differ from the process of the Sanjuro et al patent.
Flagan et al., U.S. Pat. No. 4,642,227, discloses a method for producing large particles of materials, and more particularly, to a free space reactor for producing particles greater than a few microns (preferably in the range of 10-100 microns). The processes of this invention do not employ the residence times for maintaining polysilicon particles at temperatures which reduce the hydrogen concentration as seen in the present invention.